1. Field of the Invention
The present invention relates to an RF circuit chip, an RF circuit device having the chip, and their manufacturing method. In particular, the invention relates to a shape of pads to which wires are to be connected.
2. Background Art
With the spread of portable terminal equipment, the demand for portable terminal equipment that is inexpensive and has superior RF characteristics has increased.
To decrease the size and weight of portable terminal equipment, MMICs (Monolithic Microwave ICs) are widely used as RF semiconductor chips for portable terminal equipment. MMICs are used as part of an RF semiconductor device such as a module or a package.
When an MMIC is mounted in a module, a package, or the like, the MMIC is die-bonded to a mounting substrate of the module, package, or the like, and the pads that are formed on wiring layers on the MMIC are connected to wiring layers of the module, package, or the like by using wires.
In particular, as for wires to be connected to pads (RF pads) through which an RF signal is to travel, in many cases a plurality of wires are connected to each pad and arranged parallel to each other to decrease the influence of the inductance of the wires on the RF characteristics in the RE range.
Therefore, to secure sufficient wire bonding areas, maintain the mechanical strength and the electrical characteristics of the bonding, and keep the bonding reliable, it is necessary that the width of RF pads on the MMIC be greater than that of main lines for a signal.
FIG. 14 is a plan view of part of a conventional MMIC chip.
In FIG. 14, reference numeral 100 denotes an MMIC chip; 102, a GaAs substrate; 104, a main line; 106, an RF pad; and 108, via holes that are connected to a back-surface grounding conductor. Reference numeral 110 denotes grounding pads that are grounded via the respective via holes 108.
For example, if the thickness of the GaAs substrate 102 is 100 xcexcm, it is necessary that the width of the main line 104 having a characteristic impedance of 50xcexa9 be set at about 70 xcexcm and the width of the RF pad 106 be greater than the width of the main line 104 and be set at about 150 xcexcm, for example. Although the characteristic impedance 50xcexa9 of the main line 104 is secured in this manner, in a particularly high frequency range, for example, the millimetric wave band where the frequency exceeds 60 GHz, the parallel parasitic capacitance of the RF pad 106 that is wider than the main line 104 is not negligible any more and the impedance becomes smaller than 50xcexa9, as a result of which the RF characteristics are deteriorated.
FIG. 15 is a schematic diagram showing how the RF characteristics of the conventional MMIC chip 100 are measured.
In FIG. 15, reference numeral 112 denotes a probe head and numeral 114 denotes probes that are attached to the probe head 112.
As shown in FIG. 15, the RF characteristics of the conventional MMIC chip 100 are measured and evaluated in a state that no wires are connected to it. If the RF characteristics are recognized at the designing stage with an assumption that the RF pad 106 has the same width as the main line 104, measurement results that are obtained in producing the MMIC chip 100 should be different from the RF characteristics recognized at the designing stage and the MMIC chip 100 may be judged defective.
FIG. 16 is a plan view of part of a module in which the conventional MMIC chip 100 is mounted.
In FIG. 16, reference numeral 116 denotes a module; 118, an alumina substrate; 120, a wiring layer formed on the alumina substrate 118; 122, a pad; and 124, bonding wires that connect the RF pad 106 of the MMIC chip 100 to the pad 122 on the alumina substrate 118 of the module 116.
As shown in FIG. 16, in a state that the pad 122 is connected to the RF pad 106 by the bonding wires 124, the inductance of the bonding wires 124 in the mounted state and a capacitance increase due to the increased pad width of the chip 100 partly cancel out each other and hence the RE characteristics of the mounted MMIC chip 100 would come closer to those of the MMIC 100 at the designing stage than those obtained in producing the MMIC chip 100. However, discrimination between good products and defective products is made based on evaluation results obtained in producing the MMIC chip 100, so a problem arises that an unduly large number of defective products occur.
If the RF characteristics are evaluated at the designing stage with an assumption that the pad width is greater than the line width, measurement results of the RF characteristics obtained in producing the chip 100 should coincide with the RF characteristics at the designing stage. However, the inductance of the bonding wires 124 directly influences the RF characteristics in the chip-mounted state in which the bonding wires 124 are connected to the pad 122 and the RF pad 106 and hence a problem arises that the RF characteristics obtained in the chip-mounted state no longer coincide with those at the designing stage.
If the evaluation at the designing stage is performed in a state that the bonding wires 124 are connected to the pad 122 and the RF pad 106, it is difficult to determine the RE characteristics at the designing stage because the inductance of the bonding wires 124 varies depending on their mounting states. Further, measurement results of the RE characteristics obtained in producing the chip 100 (bonding wires 124 are not connected to the pad 122 and the RE pad 106) may not coincide with the RE characteristics at the designing stage. An unduly large number of defective products may occur.
The present invention has been made to solve the above problems in the art, and a first object of the invention is therefore to provide an RF circuit chip in which variations in electrical characteristics are small by virtue of small differences in the chip electrical characteristics such as the RF characteristics at the designing stage, chip evaluation stage, and chip mounting stage while sufficient wire bonding areas are secured. A second object of the invention is to provide an RF circuit device that can be produced at a high yield and is inexpensive and highly reliable. A third object of the invention is to provide a manufacturing method capable of properly discriminating between good products and defective products by evaluating the chip RF characteristics according to the same specification as at the designing stage. A fourth object of the invention is to provide a manufacturing method capable of manufacturing, by a simple process, an RF circuit device that can be produced at a high yield and is inexpensive and highly reliable.
According to one aspect of the present invention, an RF circuit chip comprises: a first wiring layer provided on a substrate and having an end portion; first and second conductor films provided in an island-like manner adjacent to the end portion of the first wiring layer on one or both sides thereof; and a grounding conductor film provided on at least one side of the end portion with at least one of the first and second conductor films interposed in between.
According to another aspect of the present invention, an RF circuit chip comprises first wiring layers provided on a substrate so as to extend parallel with each other with a prescribed interval formed in between and having respective end portions that are adjacent to each other with an interval formed in between.
According to another aspect of the present invention, an RF circuit device comprises a dielectric substrate; an RF circuit chip provided on the dielectric substrate, the RF circuit chip comprising: a first wiring layer provided on a substrate and having an end portion; first and second conductor films provided in an island-like manner adjacent to the end portion of the first wiring layer on one or both sides thereof; and a grounding conductor film provided on at least one side of the end portion with at least one of the first and second conductor films interposed in between. The RF circuit device further comprises; a second wiring layer provided on the dielectric substrate; a first connection conductor having a first end and a second end, the first end being connected to the end portion of the first wiring layer of the RF circuit chip and the first conductor film so as to bridge those, the second end being connected to the second wiring layer; and a second connection conductor having a first end and a second end, the first end being connected to the end portion of the first wiring layer of the RF circuit chip and the second conductor film so as to bridge those, the second end being connected to the second wiring layer.
According to another aspect of the present invention, an RF circuit device comprises: a dielectric substrate; an RF circuit chip provided on the dielectric substrate and comprising first wiring layers provided on a substrate so as to extend parallel with each other with a prescribed interval formed in between and having respective end portions that are adjacent to each other with an interval formed in between; a second wiring layer provided on the dielectric substrate and to be supplied with a DC bias voltage; and a third connection conductor having a first end and a second end, the first end being connected to the end portions of the first wiring layers of the RF circuit chip so as to bridge those, the second end being connected to the second wiring layer.
Other and further objects, features and advantages of the invention will appear more fully from the following description.